During construction that involves excavation, it is prudent to determine the actual location of buried pipes, cables, gas lines, AC electric lines, sprinkler wires, CATV cable, communications wiring, and so forth. This is usually done with a portable hand-held locator that senses electromagnetic signals emitted by such buried objects. This is because maps of such buried objects, if they are available at all, are often not complete and/or accurate. Where buried utilities carry an electric signal, such as power lines, often no additional signal need be applied to perform the location. But many pipes and other conduits have no electromagnetic emission that is readily detectable. While a metal water pipe or gas pipe may, for example, re-radiate surrounding electromagnetic signals, the re-radiated signals are weak, and spread over many different frequencies. This makes the location of such buried utilities with a conventional hand-held locator very difficult. A solution is to apply an external signal from an electronic transmitter usually tuned to a specific frequency optimized for the particular application. Hand held locators with antennas, displays and audible tone generators are then used to trace the pipe, whose location is then marked on the ground or pavement with spray paint in a color which indicates whether the pipe carries water or gas, for example. Typically alligator clips attached to leads are used to apply the signal to pipes. A ground spike may be used where access to only one end of the pipe is available for connecting an alligator clip. Many buried utilities and other objects are shielded with insulation or other dielectric coating. Therefore, inductive clamps are used to induce a signal at a predetermined desired frequency without making any direct electrical connection to the metal conductor in the buried utility or other buried object.
Electronic transmitters used in locating buried pipes typically comprise a portable housing with a battery powered signal generating circuit. External jacks are used to connect cords or leads that terminate in an alligator clip or an inductive clamp. A small number of controls are provided, which may include switches for ON/OFF control, mode selection and frequency selection. The housing is usually relatively large and the storage and use of the leads, clips and ground spike are cumbersome.